The research for a comparison on the performance and characteristics of corporate mergers and acquisitions between Japan and the US,starts with an analysis of mergers between mutual banks and credit cooperatives in Japan, as the case of mergers among differenttypes offinancialinstitutions. There are 20 mergers between mutual banks and credit cooperatives, occurred during the period of 1969 and 1977. A comparison of finacial ratios between mergingbanks and correspondingpaired non-mergingbanks before and after merger, is made using financial data of 1960 to 1983 by t-test. We could find that the finacialratio, deposits per office, performsbetter after merger. Yearly comparison of ratios exhibits that gross earnings margin to total assets, loan-deposit ratio, ratio of currentexpense to currentincome, and deposit per full-time officer and employee improved after merger. Both indicate positive effect of merger. Discriminant analysis supports the result with accuracies over 63.64%. We analyzed 336 mergers of US credit unions occurred in 1986 with financial data covering the period of 1982 and 1990 supplied by National Credit Union Administration. By comparing merging and paired non-merging credit unions, net income/total assets ratio is negatively impacted by merger.A series of studies by head investigator shows negative performance by merger like mergers of credit associations, credit cooperatives and agricultural cooperatives in Japan, and US credit unions. Positive performance was examined in those mergers among different financial institutions like mutual banks and credit cooperatives, and credit associations and credit cooperatives. We need to investigative mergers among different type of financial institutions in the US and bank mergers.in both countries.これまでの研究代表者により研究では、我が国での信用金庫間の合併、信用組合間の合併、農協間の合併、あるいは米国信用組合の合併のような同種合併では合併に負の効果があり、相互銀行と信用組合、信用金庫を信用組合の合併のような異種合併では合併に正の効果があるということになる。合併戦略を考慮するのに有意義な結果である。今後、研究を拡張して、米国での異種合併、銀行合併等の研究が必要である。